1. Field of the Invention
This invention is directed to polymeric matrices designed for controlled release of biologically active substances, such as therapeutic bacteriophage which can kill bacteria capable of causing disease.
2. Review of Related Art
Bioactive composites based on biodegradable (or more precisely, bioerodible) polymers as matrices, impregnated by bactericidal substances are promising for the treatment of superficial infected wounds. On the one hand, bactericidal substances clean the wound from bacteria and make favorable conditions for wound healing, and prevent bacterial invasion through the holes made in wound coverings for exudate drainage, on the other hand, biodegradable polymer which is able to timely release enough degradation products (polymeric debris) can activate macrophages to produce the required growth factors acrd, in that way, can accelerate wound healing (Pratt, et al. (1994, xe2x80x9cDimethyltitanocene-Induced Surface Chemical Degradation of Synthetic Bioabsorbable Polyestersxe2x80x9d, J. Polym. Sci. Part 0.4: Polym. Chem., 32(5):949; Greisler, (1988), xe2x80x9cSmall Diameter Vascular Prostheses: Macrophage-Biomaterial Interactions with Bioresorbable Vascular Prosthesesxe2x80x9d. Transactions of ASAIO, 34:1051).
Mori, et al., U.S. Pat. No. 3,867,520, discloses a delivery system for therapeutic agents using films made of polyamino acid polymers with oil-like or wax-like substances dispersed in the film. Therapeutic agents are dissolved in the carrier, and when the film is applied to an internal or external surface of the body, the carrier migrates to the surface of the film where the agent is released. However, these films are not biodegraded during use.
Sidman, U.S. Pat. No. 4,351,337, discloses an implantable delivery device comprising a matrix formed of a poly-alpha-amino acid component having one or more drugs and/or diagnostic agents physically contained therein. The drug or diagnostic agent is released through diffusion and/or biodegradation resulting from the action on the polymeric matrix of enzymes present in the host into which the implant is placed.
Taniharak, et al., U.S. Pat. No. 5,770,229, discloses a medical polymer gel made up of a cross-linked polysaccharide with a drug attacked to the polysaccharide via a linkage that is cleavable by an endogenous enzyme. This system provides for delayed release of the attached drug from the polymer, but the release rate is subject to individual variation in the amount of the endogenous enzyme, and the polymer, while biocompatible, is not biodegradable.
Kuroyangi and coworkers (1992, J. Appl. Biomater., 3:153-161) have developed a wound dressing for burn care that is a hydrophobic poly-L-leucine spongy matrix impregnated with antibacterial silver sulfadiazine supported by a fine nylon mesh. This wound dressing suppresses bacterial growth while controlling fluid loss. However, the dressing is not degraded, but rather sticks to the wound until it separates spontaneously from the healed skin.
Georgian Patent No. 1090 describes a wound dressing containing 45-50 wt. % biodegradable poly(ester-amide) based on natural alpha-amino acids impregnated with 50-55 wt. % dried bacteriophage. The poly(ester-amide) is not characterized in detail, but the dressing also has 0.05-0.15 wt. % surface immobilized alpha-chymotrypsin. The impregnated poly(ester-amide) is formed into a film, and the film is used to accelerate healing of superficial wounds, including burns.
Tsitlanadze, et al., in an abstract from Int. Symp. Biodegrad. Mater, Oct. 7-9, 1996, Hamburg, Germany, describe alpha-chymotrypsin-catalyzed hydrolysis of regular poly(ester-amides) (PEAs) of general formula I: 
where
k=2, 3, 4, or 6
m=4 or 8, and
R=CH(CH3)2, CH2CH(CH3)2, CH(CH3)CH2CH3, (CH2)3CH3, CH2C6H5, or (CH2)3SCH3.
It is reported that alpha-chymotrypsin is spontaneously immobilized on the surface of the PEAs from aqueous solution, and erodes the polymer surface under physiologic conditions, with increasing lysis for more hydrophobic R groups and more hydrophobic polymer backbone. A biocomposite material based on a PEA polymer containing bacteriophages, antibiotic or anesthetic was prepared for study as artificial skin for healing burns and festering wounds.
The present invention provides bioerodable constructs for controlled release of bioactive materials. In a preferred mode, the constructs may be utilized adjacent to a biological surface. The constructs are based on a blend of two or more poly(ester-amide) polymers (PEA). Such polymers may be prepared by polymerization of a diol (D), a dicarboxylic acid (C) and an alpha-amino acid (A) through ester and amide links in the form (DACA)n. An example of a (DACA)n polymer is shown below in formula II. Suitable amino acids include any natural or synthetic alpha-amino acid, preferably neutral amino acids.
Diols may be any aliphatic diol, including alkylene diols like HOxe2x80x94(CH2)kxe2x80x94OH (i.e. non-branched), branched diols (e.g., propylene glycol), cyclic diols (e.g. dianhydrohexitols and cyclohexanediol), or oligomeric diols based on ethylene glycol (e.g., diethylene glycol, triethylene glycol, tetraethylene glycol, or poly(ethylene glycol)s). Aromatic diols (e.g. bis-phenols) are less useful for these purposes since they are more toxic, and polymers based on them have rigid chains that are less likely to biodegrade.
Dicarboxylic acids may be any aliphatic dicarboxylic acid, such as xcex1,xcfx89-dicarboxylic acids (i.e., non-branched), branched dicarboxylic acids, cyclic dicarboxylic acids (e.g. cyclohexanedicarboxylic acid). Aromatic diacids (like phthalic acids, etc.) are less useful for these purposes since they are more toxic, and polymers based on them have rigid chain structure, exhibit poorer film-forming properties and have much lower tendency to biodegrade.
Preferred PEA polymers have the formula II: 
where
k=2-12, especially 2, 3, 4, or 6,
m=2-12, especially 4 or 8, and
R=CH(CH3)2, CH2CH(CH3)2, CH(CH3)CH2CH3, (CH2)3CH3, CH2C6H5, or (CH2)3SCH3.
The constructs optionally contain bioactive inclusions, which are released upon degradation (bioerosion) of the construct.
In a preferred embodiment, this invention provides biodegradable constructs which comprise a first PEA polymer in which A is L-phenylalanine (Phe-PEA) and a second PEA polymer in which A is L-leucine (Leu-PEA). Preferably, the ratio of Phe-PEA to Leu-PEA is from 10:1 to 1:1; more preferably, the ratio of Phe-PEA to Leu-PEA is from 5:1 to 2.5:1. The construct may be formed as a deformable sheet adapted to conform to a biological surface.
In another embodiment, this invention provides bioerodable constructs comprising PEA polymers and further comprising a bioactive agent, which may be selected from the group consisting of antiseptics, anti-infectives, such as bacteriophages, antibiotics, antibacterials, antiprotozoal agents, and antiviral agents, analgesics, anti-inflammatory agents including steroids and non-steroidal anti-inflammatory agents including COX-2 inhibitors, anti-neoplastic agents, contraceptives, CNS active drugs, hormones, and vaccines.
In yet another embodiment, the bioerodable construct of this invention comprises an enzyme capable of hydrolytically cleaving the PEA polymer, such as xcex1-chymotrypsin. In a preferred embodiment, the enzyme is adsorbed on the surface of the construct. In a particularly preferred embodiment, the construct contains bacteriophage which are released by action of the enzyme.
This invention also provides a method of treating a patient having an ulcerative wound comprising inserting into the wound or covering the wound with a bioerodable construct according to claim 1, wherein the bioerodable construct contains a bioactive agent, which may be bacteriophage, an antibiotic, an antiseptic, or an analgesic. The wound treated by this invention may be open or infected, and the construct may be in the form of a deformable sheet. In a preferred embodiment, the construct used in treatment of the wound contains bacteriophage specific for bacteria found in the wound. The construct may also comprise an enzyme capable of hydrolytically cleaving the PEA polymer.
There is no currently available biodegradable polymer or polymeric blend composed entirely of naturally occurring and nontoxic building blocks showing high plasticity (e.g., pliability when hydrated) together with high enzyme-catalyzed biodegradation rates, solubility in common organic solvents like chloroform, and suitable for either impregnation or the spontaneous surface immobilization (adsorption) of the enzymes like trypsin, a-chymotrypsin, and lipase. The polymeric blends of this invention provide all of these properties, permitting their use as matrices for wound dressing/healing devices which are plastic and act to release bioactive substances in a sustained/controlled fashion.